I've seen some interesting numbers like "93% as strong", whatever that means.
I have an 870 Express with a MIM extractor. I've stressed the thing pretty badly with shells that had been sized wrong.
Repeatedly extracting badly-stuck spent 12 Gauge hulls by slamming the buttstock on a bench is a lot more stress than an extractor normally experiences!
The thing is still as good as new. It looks, feels and works like new. We'll see after
another 10 or 20 thousand rounds if that's still true.
I also have a higher end gun with the same basic bolt design -- an 1100. It has a machined extractor. It also works fine after 35 years. I'll get back to you when the 870 is that old and tell you how many extractors it ate up.
AFAIK you can forge something badly, you can machine it badly (I've had a far less delicate machined part break on a .22 rifle after a few bricks). You can MIM a part badly. Or you can make the part well, with good metal and good methods.
It is likely that MIM cannot replicate the quality of the best forgings or the best machined stock. If you pay top dollar for the best possible gun (like one o' dem high-falutin' $2500 1911 pistols), you can get better absolute quality from tried and true forging and machining.
But that doesn't mean a specific MIM part is any weaker than the average production part made with other methods. MIM steel has come a long way. However, there are probably parts where it is a good idea, and parts where it's a bad idea, no matter how refined the process has become.
